1. Field of the Invention
This invention relates to a method for the production of a semiconductor wafer, particularly a single crystal silicon wafer (hereinafter referred to simply as "wafer").
2. Prior Art Statement
Generally, the method for the production of a wafer comprises a slicing step for slicing a single crystal ingot pulled up by a single crystal pulling device thereby obtaining wafers of the shape of a thin disc, a chamfering step for chamfering the peripheral edge part of the wafer obtained by the slicing step thereby preventing the wafer from cracking or chipping, a lapping step for lapping the chamfered wafer thereby flattening the surface thereof, an etching step for depriving the lapped wafer of residual mechanical strain, a surface-polishing step for polishing one surface of the etched wafer, and a cleaning step for cleaning the polished wafer thereby removing abrasive and foreign matter adhering thereto.
The wafer which is produced after the various steps mentioned above, however, entails the following objectionable effects because an etched surface remains forever on the reverse side thereof.
A mixed acid is generally used as the etchant for the etching step mentioned above. When the etching treatment of a wafer is carried out by the use of this mixed acid, a large undulation W1 having a period in the approximate range of 0.5 to 1 mm and a P-V (peak to valley) value in the approximate range of 0.1 to 0.5 .mu.m, the magnitudes peculiar to the mixed acid, persists on the reverse side of a wafer W which has not undergone the surface polishing mentioned above as illustrated in FIG. 5 (a) (depicting the wafer W in a free state).
When the reverse side of the wafer W is fastened to a chucking plate 10 at the step of photolithography in the process of production of a device, the undulation W1 mentioned above on the reverse side transfers toward the obverse side and gives rise to an undulation W1' on the obverse side as illustrated in FIG. 5 (b). This undulation W1' degrades the resolution of exposure and consequently causes a decline in the yield of the device.
As means to solve the problem mentioned above, the method of polishing both the obverse and the reverse sides of the wafer W as illustrated in FIG. 6 (a) may be conceived. In accordance with this method, since the undulation W1 illustrated in FIG. 5 (a) is absent from the reverse side of the wafer W, the problem mentioned above does not arise even when the reverse side of the wafer W is fastened through aspiration to the chucking plate 10 as illustrated in FIG. 6 (b) at the step of photolithography.
According to the method involving the polishing of both sides as described above, since the reverse side of the wafer W acquires a mirror surface, the problem arises that the popular wafer sensor which is capable of detecting the presence of a wafer by the scattering of light fails to detect the wafer W. When the wafer W is fastened through aspiration to the chucking plate 10, since an extraneous particle P accidentally adhering to the reverse side of the wafer W and intervening between the wafer W and the chucking plate 10 elastically deforms the wafer W as illustrated in FIG. 6 (c), the same problem as mentioned above ensues that the part of the obverse surface of the wafer W which overlies the extraneous particle P forms a protuberance W2 and undulates the obverse surface of the wafer W.
This invention, produced by an urge to eliminate the problem mentioned above, has for its object the provision of a method for the production of a wafer which permits detection by a sensor, avoids degrading the resolution of exposure at the step of photolithography during the process of manufacture of a device, and improves the yield of the device.